diff --git a/.obsidian/graph.json b/.obsidian/graph.json
index 5321fcd..4144d8b 100644
--- a/.obsidian/graph.json
+++ b/.obsidian/graph.json
@@ -32,6 +32,6 @@
   "repelStrength": 10,
   "linkStrength": 1,
   "linkDistance": 250,
-  "scale": 1.166549028490861,
+  "scale": 0.9752800867986091,
   "close": true
 }
\ No newline at end of file
diff --git a/CS notes/pages/Leetcode  Valid-Parentheses.md b/CS notes/pages/Leetcode  Valid-Parentheses.md
index ee0a22a..a9ee0e9 100644
--- a/CS notes/pages/Leetcode  Valid-Parentheses.md	
+++ b/CS notes/pages/Leetcode  Valid-Parentheses.md	
@@ -19,17 +19,84 @@ tag:#stack
  
 
 ##### Links:
-- [Link to problem]()
+- [Link to problem](https://leetcode.com/problems/valid-parentheses/)
 ___
 ### Problem
+Given a string `s` containing just the characters `'('`, `')'`, `'{'`, `'}'`, `'['` and `']'`, determine if the input string is valid.
+
+An input string is valid if:
+
+1.  Open brackets must be closed by the same type of brackets.
+2.  Open brackets must be closed in the correct order.
 
 #### Examples
+**Example 1:**
 
+```markdown
+**Input:** s = "()"
+**Output:** true
+```
+
+**Example 2:**
+
+```markdown
+**Input:** s = "()[]{}"
+**Output:** true
+```
+
+**Example 3:**
+
+```markdown
+**Input:** s = "(]"
+**Output:** false
+```
 #### Constraints
+-   `1 <= s.length <= 104`
+-   `s` consists of parentheses only `'()[]{}'`.
 
 ### Thoughts
 
-> [!summary]
-> This is a #template_remove_me
-
+Basic stack usage. 
+Can be implemented using std_stack or stc_vector.
+obviously i should use std_stack.
 ### Solution
+
+```cpp
+class Solution {
+public:
+  bool isValid(string s) {
+    vector<char> stack;
+    vector<vector<char>> pairs = {{'(', ')'}, {'{', '}'}, {'[', ']'}};
+
+    int loc;
+    const int size = pairs.size();
+    for (char c : s) {
+
+      for (loc = 0; loc < size; loc++) {
+        if (c == pairs[loc][1]) {
+          if (stack.empty()) {
+            // if there is no {([ before
+            printf("No {([ before.\n");
+            return false;
+          } else if (stack.back() == pairs[loc][0]) {
+            stack.pop_back();
+          } else {
+            // parens mismatch
+            printf("parens mismatch: %c %c\n", stack.back(), pairs[loc][0]);
+            return false;
+          }
+        } else if (c == pairs[loc][0]) {
+          stack.push_back(c);
+        }
+      }
+    }
+
+    if (stack.empty()) {
+      return true;
+    } else {
+      return false;
+    }
+  }
+};
+
+```
\ No newline at end of file
diff --git a/CS notes/pages/Leetcode Remove-Duplicates-From-Sorted-List.md b/CS notes/pages/Leetcode Remove-Duplicates-From-Sorted-List.md
index 2113ce7..6e0cba8 100644
--- a/CS notes/pages/Leetcode Remove-Duplicates-From-Sorted-List.md	
+++ b/CS notes/pages/Leetcode Remove-Duplicates-From-Sorted-List.md	
@@ -16,16 +16,39 @@
 tag:#linked_list
 ```
  
+- [[Floyd's Cycle Finding Algorithm]]
+- [[Leetcode Linked-List-Cycle]]
+- [[Leetcode Merge-Two-Sorted-Lists]]
+- [[Leetcode Remove-Linked-List-Elements]]
+- [[Leetcode Reverse-Linked-List]]
+- [[Two pointers approach]]
  
 
 ##### Links:
-- [Link to problem]()
+- [Link to problem](https://leetcode.com/problems/remove-duplicates-from-sorted-list/)
 ___
 ### Problem
+Given the `head` of a sorted linked list, _delete all duplicates such that each element appears only once_. Return _the linked list **sorted** as well_.
 
 #### Examples
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2021/01/04/list1.jpg)
+
+**Input:** head = [1,1,2]
+**Output:** [1,2]
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2021/01/04/list2.jpg)
+
+**Input:** head = [1,1,2,3,3]
+**Output:** [1,2,3]
 
 #### Constraints
+-   The number of nodes in the list is in the range `[0, 300]`.
+-   `-100 <= Node.val <= 100`
+-   The list is guaranteed to be **sorted** in ascending order.
 
 ### Thoughts